The present invention relates to a capacitor for use in semiconductor integrated circuit devices for communication, etc. and a method for fabricating the capacitor.
Semiconductor integrated circuit devices for communication include a large number of capacitors having large areas and large capacitances. Accordingly, it is important how to increase breakdown voltage yield and reliability of the capacitors.
A conventional method for fabricating a capacitor used in semiconductor integrated circuit devices for communication will be explained with reference to FIGS. 14A-14C and 15A-15B.
An Au (gold) film, for example, is deposited on a substrate 100 and patterned to form a lower electrode 102 (FIG. 14A).
Next, a silicon nitride film 104 which functions as an interconnection cover film and a capacitor dielectric film is formed on the substrate 100 with the lower electrode 102 formed on (FIG. 14B).
Then, an inter-layer insulation film 106 of benzocyclobutene (hereinafter also called BCB) or polyimide (hereinafter also called PI) is formed on the silicon nitride film 104.
Then, a silicon nitride film 108 is deposited on the inter-layer insulation film 106 and patterned (FIG. 14C).
Next, with the silicon nitride film 108 as a mask, the inter-layer insulation film 106 is etched to form an opening 110 reaching the silicon nitride film 104 (FIG. 15A). The etching of the inter-layer insulation film 106 is, e.g., plasma etching using a gas of oxygen with a trace of fluorine-based gas added to. The plasma etching is followed by wet processing using a hydrofluoric acid-based chemical solution as processing for removing residual silicon produced upon the etching.
Then, an upper electrode 112 is formed on the silicon nitride film 104 exposed in the opening 110, extended over the inter-layer insulation film 106 (FIG. 15B).
A capacitor comprising the lower electrode 102, the capacitor dielectric film of the silicon nitride film 104 and the upper electrode 112 has been thus fabricated.
In the above-described method for fabricating conventional capacitor, in etching the inter-layer insulation film 106 to form the opening 110, the lower silicon nitride film 104 is exposed to the etching atmosphere. Considering fluctuation of film thickness, etc., a prescribed over etching is conducted in etching the inter-layer insulation film 106.
Accordingly, the silicon nitride film 104 is damaged in etching the inter-layer insulation film 106. Resultantly, the silicon nitride film 104 has distributed film decreases or is damaged, which has made it impossible to form a capacitor of high accuracy and reliability.
An object of the present invention is to provide a capacitor having high capacitance value controllability and reliability, and a method for fabricating the capacitor.
According to one aspect of the present invention, there is provided a capacitor comprising: a lower electrode formed on a substrate; an insulation film formed on the substrate with the lower electrode formed on, and having an opening on the lower electrode; a capacitor dielectric film formed on the lower electrode in the opening, and having a larger film thickness at a peripheral part of the opening than at a central part of the opening; and an upper electrode formed on the capacitor dielectric film.
According to another aspect of the present invention, there is provided a capacitor comprising: a lower electrode formed on a substrate; a first insulation film formed on the substrate with the lower electrode formed on, and having a first opening on the lower electrode; a second insulation film formed on the first insulation film, and having a second opening in a region where the first opening is formed; a capacitor dielectric film formed on the lower electrode in the opening, and extended over the second insulation film; and an upper electrode formed on the capacitor dielectric film.
According to further another aspect of the present invention, there is provided a method for fabricating a capacitor comprising the steps of: forming a lower electrode on a substrate; forming a first insulation film on the substrate with the lower electrode formed on; forming a second insulation film on the first insulation film; forming an opening reaching the lower electrode in the first insulation film and the second insulation film; forming a capacitor dielectric film on the lower electrode, extended over the second insulation film; and forming an upper electrode on the capacitor dielectric film.
As described above, according to the present invention, the capacitor dielectric film is formed after the opening for exposing the lower electrode is formed in the inter-layer insulation film 16, whereby the capacitor dielectric film can be kept from being exposed to the etching atmosphere. Thus, the intra-distribution and fluctuation of the film thickness of the capacitor dielectric film, and degradation of the film quality can be prevented.
The capacitor dielectric film is thicker selectively at a peripheral part of the opening formed in the inter-layer insulation film, whereby degradation of breakdown voltage, stress resistance, etc. due to the coverage of the capacitor dielectric film can be suppressed.
The opening is formed in the inter-layer insulation film in a large area containing a region for the lower electrode formed in, whereby even when the peripheral part of the opening has parts of poor coverage of the capacitor dielectric film, the parts are away from between the lower electrode and the upper electrode. Accordingly, the capacitor dielectric film can be highly reliable in breakdown voltage, stress resistance, etc.